The invention relates to an intrusion detection process by emission and reception of waves in a space, such as the space defined by the passenger compartment of an automobile vehicle or a room or compartment of a building.
The invention also includes an intrusion detection device that implements the process according to the invention.
Known vehicle intruision detection systems are nonnally activated each time the vehicle is locked. The locking is achieved by means known to professionals of the art, for example by radio means, or a key or a classic mechanical switch. Once the intrusion detection system is activated, it monitors the space in order to detect a possible intrusion. If this detection meets certain criteria, the system then sets off an alarm, for example an audible siren or horn. The system can be inhibited by unlocking, or any other means, to give the owner access to the vehicle.
Prior-art intrusion detection techniques are generally based on the emission of acoustic waves (for example at ultrasound frequencies) or electromagnetic waves (for example radar) and the system functions by exploiting the Doppler effect. These systems include a transmitter which, when activated, emits a wave in the form of a single-frequency signal filling the inside of the vehicle. A receiver detects any frequency shift due to the Doppler effect of the wave reflected inside the vehicle. The characteristics of the signal received are analyzed and compared with one or more reference values. This frequency shift is characteristic of the reflection of the emitted signal from a moving object, which probably indicates an intrusion. The system then triggers an alarm.
However, these intrusion detection techniques do not completely avoid the risk of false alarms. In particular, disturbances such as sound waves, shocks on the roof or windows of the vehicle, etc. can cause modulation of the emitted wave. This modulated wave, after processing and analysis by the receiver can be incorrectly interpreted as an intrusion, since the characteristics of the modulated wave may be identical to those of the wave reflected from a moving object inside the vehicle.
Wave-generating disturbances other than those associated with an intruder may therefore result in modulation of the acoustic waves inside the vehicle. This modulation, after analysis, is interpreted as an intrusion and an alarm is set off. Such false alarms are extremely undesirable and a considerable nuisance.
In order to reduce this risk of false alarms, such a system could be made less sensitive in order to ignore signals presumed to have been caused by anything other than the actual movement of an object. However, this compromise between sufficient sensitivity to detect a movement and desensitization to ignore sources of parasitic interference is difficult to achieve and therefore unsatisfactory.
It is therefore desirable to design an intrusion detection system that is sensitive to intrusions yet able to avoid false alarms caused by non-intrusion disturbances.
The object of the present invention is therefore to propose an automobile vehicle intrusion detection system making use of emission and reception of acoustic or electromagnetic waves, but which overcomes the various drawbacks of prior-art systems.
For this purpose, the invention proposes an intrusion detection process for detecting an intrusion within a space, in which:
at least two acoustic or electromagnetic signals are emitted at different frequencies (f1, f2, . . . fn) inside said space;
at a point inside said space, a signal is received that is the combination of the signals emitted and reflected in said space;
the characteristics of the demodulated signals of different frequencies are compared to establish the presence or absence of an intrusion;
an intrusion signal is generated when the presence of an intruder is confirmed.
The process is advantageously completed by the following characteristics that may be taken one at a time or in their technically possible combinations:
the characteristics of the demodulated signals of different frequencies are the frequency shift, the amplitude, the phase or the duration, and the number of revolutions and the perimeter of the demodulation;
the presence of an intruder is established when the frequency shift of the demodulated signals, for each of the carrier frequencies, is different;
the demodulator used to demodulate the signals received is an IQ demodulator;
the decision on the presence or absence of an intruder is based on a comparison of some or all of the characteristics of the demodulated signals of different frequencies between themselves and/or relative to a threshold;
the decision on the presence or absence of an intruder, after comparison of some or all of the characteristics of the demodulated signals of different frequencies, is based on the relative number of xe2x80x9cpositivexe2x80x9d and xe2x80x9cnegativexe2x80x9d comparisons;
the forward and/or rearward direction of movement and the speed of the moving object in said space can be determined;
one or more frequencies of the emitted signals is a harmonic frequency of one of the other frequencies;
one or more frequencies of the emitted signals is an ultrasound or electromagnetic frequency;
the process includes an initial stage of self-configuration of the system;
the emission and/or reception of the signals is simultaneous or alternating;
the emission and/or of reception is performed by a transducer that emits and/or receives signals at different frequencies;
the emission and reception steps are performed by a single transducer that emits and receives signals at different frequencies either simultaneously or alternating.
The invention also proposes a device that implements this process. This device includes:
a transmitter that can emit at least two acoustic or electromagnetic signals at different frequencies;
a receiver that receives an acoustic or electromagnetic signal that is the combination of the signals emitted and reflected in said space;
means of processing and comparing the characteristics of the demodulated signals of different frequencies in order to generate an intrusion signal based on this comparison.
The device offers numerous advantageous characteristics:
it includes adding and/or amplification means to add and/or amplify the acoustic or electromagnetic signals of different frequency before emission;
said processing means include filtering and/or amplification means to isolate the characteristics of the demodulated signals of different frequencies;
said transmitter and/or receiver is a transducer that emits and/or receives signals at different frequencies simultaneously, sequentially, alternately or separately.
Other advantageous characteristics of the device according to the invention relate to an analysis involving several cumulative criteria such as the amplitude, phase, frequency and frequency shift of the detected signal.
The general principle applied by the system to detect an intrusion is to transmit signals in said space and analyze the resultant signals after reflection in this space. A difference between the resultant and original signals meeting certain criteria is taken as an indication of intrusion. Said signals, preferably acoustic, are emitted at different frequencies and the signals resulting from these emissions are examined. One of these frequencies can be a harmonic frequency of one of the other frequencies. One or more of the frequencies can be an ultrasound frequency, but other frequencies can be used.
In this manner, the proposed system is able to distinguish false alarms from actual intrusions by using two or more frequencies:
in the event of an intrusion, revealed by the presence of a moving object in said space, frequency shifts caused by the intruder are observed, and these frequency shifts are different (owing to the Doppler effect) for each of the carrier frequencies;
in the case of a disturbance due to xe2x80x9cnoisexe2x80x9d (thermal shock, sound noise, impacts, etc.), the modulation of the acoustic waves inside said space is identical at each of the carrier frequencies.